Financial Data of Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) Segment	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Lease Income	$ 284.5	$ 278.3
Cargo and Freight Revenue	20.3	24.2
Provision for Income Taxes, Equity Method Investment	$ 2.7	3.0
Number of business segments | Segment	4
Profitability
Other revenue	$ 29.6	17.2
Maintenance expense	78.5	78.3
Depreciation expense	69.3	68.5
Marine operating expense	12.3	18.9
Operating lease expense	16.8	20.7
Other operating expense	8.8	7.3
Total Expenses	185.7	193.7
Disposition gains on owned assets	20.0	37.9
Residual sharing income	1.8	1.8
Nonremarketing disposition gains	1.4	5.7
Asset impairment	0.0	(0.1)
Net gain on asset dispositions	23.2	45.3
Interest Revenue (Expense), Net	(37.2)	(40.9)
Other (expense) income	(3.3)	(4.0)
Income (Loss) From Equity Method Investment, Before Tax	10.2	11.5
Segment profit (loss)	141.6	137.9
SG&A	38.8	45.7
Income tax benefit	30.8	27.0
Net Income	69.3	62.2
Revenues	334.4	319.7
Selected Balance Sheet Data
Portfolio Investments and Capital Additions	140.2	180.9
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	356.3		$ 348.5
Identifiable assets	7,062.0		6,894.2
Rail North America [Member]
Segment Reporting Information [Line Items]
Lease Income	236.6	228.5
Cargo and Freight Revenue	$ 0.0	0.0
Leverage level expressed as a ratio of recourse debt to equity	5
Profitability
Other revenue	$ 27.8	14.7
Maintenance expense	65.8	69.2
Depreciation expense	56.5	52.3
Marine operating expense	0.0	0.0
Operating lease expense	16.8	20.7
Other operating expense	6.9	5.5
Total Expenses	146.0	147.7
Disposition gains on owned assets	17.6	35.9
Residual sharing income	0.3	0.2
Nonremarketing disposition gains	0.7	0.7
Asset impairment	0.0	0.0
Net gain on asset dispositions	18.6	36.8
Interest Revenue (Expense), Net	(27.2)	(24.5)
Other (expense) income	(1.3)	(2.2)
Income (Loss) From Equity Method Investment, Before Tax	0.2	0.2
Segment profit (loss)	108.7	105.8
Revenues	264.4	243.2
Selected Balance Sheet Data
Portfolio Investments and Capital Additions	112.9	129.8
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	10.9		(12.0)
Identifiable assets	4,756.5		(4,629.1)
Rail International [Member]
Segment Reporting Information [Line Items]
Lease Income	44.9	42.1
Cargo and Freight Revenue	$ 0.0	0.0
Leverage level expressed as a ratio of recourse debt to equity	2
Profitability
Other revenue	$ 1.6	1.9
Maintenance expense	12.5	8.9
Depreciation expense	11.1	10.7
Marine operating expense	0.0	0.0
Operating lease expense	0.0	0.0
Other operating expense	1.4	0.9
Total Expenses	25.0	20.5
Disposition gains on owned assets	0.0	0.0
Residual sharing income	0.0	0.0
Nonremarketing disposition gains	0.7	5.0
Asset impairment	0.0	(0.1)
Net gain on asset dispositions	0.7	4.9
Interest Revenue (Expense), Net	(7.3)	(6.5)
Other (expense) income	(2.2)	0.0
Income (Loss) From Equity Method Investment, Before Tax	(0.1)	(0.1)
Segment profit (loss)	12.6	21.8
Revenues	46.5	44.0
Selected Balance Sheet Data
Portfolio Investments and Capital Additions	22.0	41.4
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	1.4		(1.4)
Identifiable assets	1,194.2		(1,117.6)
ASC [Member]
Segment Reporting Information [Line Items]
Lease Income	1.0	1.0
Cargo and Freight Revenue	$ 4.1	7.0
Leverage level expressed as a ratio of recourse debt to equity	1.5
Profitability
Other revenue	$ 0.0	0.0
Maintenance expense	0.2	0.2
Depreciation expense	0.0	0.0
Marine operating expense	2.9	6.9
Operating lease expense	0.0	0.0
Other operating expense	0.0	0.0
Total Expenses	3.1	7.1
Disposition gains on owned assets	0.0	0.0
Residual sharing income	0.0	0.0
Nonremarketing disposition gains	0.0	0.0
Asset impairment	0.0	0.0
Net gain on asset dispositions	0.0	0.0
Interest Revenue (Expense), Net	(1.1)	(1.3)
Other (expense) income	0.0	0.0
Income (Loss) From Equity Method Investment, Before Tax	0.0	0.0
Segment profit (loss)	0.9	(0.4)
Revenues	5.1	8.0
Selected Balance Sheet Data
Portfolio Investments and Capital Additions	4.7	9.3
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0.0		0.0
Identifiable assets	278.6		(284.7)
Portfolio Management [Member]
Segment Reporting Information [Line Items]
Lease Income	2.0	6.7
Cargo and Freight Revenue	$ 16.2	17.2
Leverage level expressed as a ratio of recourse debt to equity	3
Profitability
Other revenue	$ 0.2	0.6
Maintenance expense	0.0	0.0
Depreciation expense	1.7	5.5
Marine operating expense	9.4	12.0
Operating lease expense	0.0	0.0
Other operating expense	0.5	0.9
Total Expenses	11.6	18.4
Disposition gains on owned assets	2.4	2.0
Residual sharing income	1.5	1.6
Nonremarketing disposition gains	0.0	0.0
Asset impairment	0.0	0.0
Net gain on asset dispositions	3.9	3.6
Interest Revenue (Expense), Net	(2.2)	(5.2)
Other (expense) income	0.0	0.0
Income (Loss) From Equity Method Investment, Before Tax	10.1	11.4
Segment profit (loss)	18.6	15.9
Revenues	18.4	24.5
Selected Balance Sheet Data
Portfolio Investments and Capital Additions	0.0	0.0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	344.0		335.1
Identifiable assets	605.8		636.5
Other [Member]
Segment Reporting Information [Line Items]
Lease Income	0.0	0.0
Cargo and Freight Revenue	0.0	0.0
Profitability
Other revenue	0.0	0.0
Maintenance expense	0.0	0.0
Depreciation expense	0.0	0.0
Marine operating expense	0.0	0.0
Operating lease expense	0.0	0.0
Other operating expense	0.0	0.0
Total Expenses	0.0	0.0
Disposition gains on owned assets	0.0	0.0
Residual sharing income	0.0	0.0
Nonremarketing disposition gains	0.0	0.0
Asset impairment	0.0	0.0
Net gain on asset dispositions	0.0	0.0
Interest Revenue (Expense), Net	0.6	(3.4)
Other (expense) income	0.2	(1.8)
Income (Loss) From Equity Method Investment, Before Tax	0.0	0.0
Segment profit (loss)	0.8	(5.2)
Revenues	0.0	0.0
Selected Balance Sheet Data
Portfolio Investments and Capital Additions	0.6	0.4
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0.0		0.0
Identifiable assets	226.9		$ 226.3
Parent [Member]
Profitability
Income tax benefit	$ 33.5	$ 30.0